Proteins, plant gums, and other substances that contain amino acids were identified in paints and gesso samples by a mathematical procedure for evaluating amino acid composition data. Correlation coefficient calculations were suitable for samples containing one amino acid-containing substance. For samples suspected of containing a mixture of two substances composed of amino acids, algebraic equations were used to identify the substances and to estimate the composition. Samples from the wall paintings of the St. Juda church in Prague, tested by gas chromatographic analysis of amino acid-ethyl chloroformate derivatives, were found to contain casein, or admixtures of animal glue and egg tempera. Using the procedure, data from two published high-performance liquid chromatography studies of paint and gessoes were re-evaluated. Although many of the original findings were supported, there was reason to suspect that some samples, originally believed to contain a single proteinaceous material, may also contain a second. -- ICCROM